1. Field of the Invention
This invention relates to rubber compositions containing ethylene-propylene-diene terpolymers (referred to as EPDM) or ethylene-propylene copolymers (referred to as EPR) and silicones.
2. Description of the Prior Art
Various attempts have been made to compensate for the insufficient strength of silicone rubber with EPDM or EPR, and at the same time to compensate for the insufficient heat resistance of EPDM or EPR with silicone rubber. Safford, in U.S. Pat. No. 3,227,777, issued Jan. 4, 1966, describes a mixture of a copolymer of ethylene and propylene, an alkenylpolysiloxane, and an organic peroxide which can be vulcanized to a rubbery material. Falender et al., in U.S. Pat. No. 3,865,897, describes a method of making a blend by mechanically mixing certain polyolefins, such as polyethylene, and a polydiorganosiloxane gum containing vinyl or allyl radicals. The mixing method requires shearing at elevated temperatures to form grafting between the two types of polymers. The resulting blend can be crosslinked by a variety of means including organic peroxide. Falender et al. relate to blends of polydiorganosiloxane gum with thermoplastic polyolefins. Walters, in U.S. Pat. No. 3,979,356, issued Sept. 7, 1976, describes an ethylene-vinyl acetate copolymer blended with silicone elastomer and then cured with organic peroxide.
Betts et al., in U.S. Pat. No. 4,123,586, issued Oct. 31, 1978, describes improving the resistance to flame of ethylene-containing polymers, such as ethylene-propylene copolymers, ethylene-propylene diene terpolymers, ethylene-vinyl acetate, ethylene alkyl-acrylate copolymers, and ethylene-butene copolymers. The ethylene-containing polymers are mixed with fillers, pigments, curing coagents, antioxidants, modifying agents, mold release ingredients, processing aids or lubricants such as lead or zinc stearates in amounts of 1 to 5 parts by weight, and essential ingredients, such as decabromodiphenyl ether, silicone gum in amounts of 3 to 10 parts by weight and dibasic lead. Betts et al. show curing with organic peroxide. Betts et al. also show, in an example for 6.25 parts by weight of silicone gum, a tensile strength retention after heating for seven days at 150.degree. C. of 88%, and an elongation retention of 91%.
As shown above, certain compositions are described where unvulcanized EPDM or EPR is compounded with organopolysiloxane gum or unvulcanized silicone rubber and subsequently vulcanizing the mixture with an organic peroxide. The inventor described in U.S. Pat. No. 4,234,702, issued Nov. 18, 1980, filed Mar. 21, 1979, (Belgium Pat. No. 875,702, granted Oct. 19, 1979) adding an organopolysiloxane possessing a C.sub.4 -C.sub.20 alkyl radical to a compounded rubber system consisting of natural or synthetic organic rubber including unvulcanized EPDM or EPR and an organopolysiloxane gum or unvulcanized silicone rubber, and obtaining a compounded rubber composition which exhibits excellent heat resistance and strength, thus overcoming the drawbacks of both polymers.
However, when this compounded rubber is used in industry, it must be adhered to a metallic part or a synthetic resin part using a room-temperature, moisture-curable type silicone rubber. Here, adhesiveness between the compounded rubber and the room-temperature, moisture-curable type silicone rubber is poor and peeling occurs easily. The inventors earnestly investigated the compounded rubbers in an attempt to overcome these drawbacks, and this invention was achieved based on the results of the investigation.